As is well known, fluids such as crude oil, water, etc., are typically pumped from wells to the surface by means of down hole pumps. Perhaps the most widely utilized type of down hole pump includes a standing valve located at the bottom of the well and a traveling valve located above the standing valve for reciprocation under the action of a pumping unit. The standing valve and the traveling valve each include a ball check valve.
As the traveling valve is moved upwardly by the pumping unit, the ball check valve thereof closes thereby causing fluid situated above the traveling valve to be moved upwardly. Simultaneously, the ball check valve of the standing valve opens thereby allowing fluid to enter the portion of the well located between the standing valve and the traveling valve. As the traveling valve moves downwardly under the action of the pumping unit, the ball check valve thereof opens thereby allowing fluid to pass through the traveling valve so that it can be lifted upwardly upon the next reciprocation thereof. Meanwhile, the ball check valve of the standing valve closes thereby preventing downward movement of fluid therethrough.
Ball check valves typically include a cage and a ball positioned in the cage for reciprocation to open and close the valve. Heretofore, many ball check valves have utilized cage assemblies including components which are threadedly interconnected. It has been found that such threaded connections are prone to premature failure under the stresses imposed by pumping operations. Any such failure requires the removal of the down hole pump incorporating the ball check valve to the surface for disassembly and repair, a costly and time-consuming operation. The use of conventional welding techniques to join the component parts of the cage assembly of a ball check valve leads to similar problems.
The present invention comprises an improved cage assembly for ball check valves which overcomes the foregoing and other problems long since associated with the prior art. In accordance with the broader aspects of the invention, the cage assembly of a ball check valve includes a ball receiving insert formed from a hard, tough, wear-resistant material. The ball receiving insert is received in a cavity formed in the lower end of the upstream housing of the ball check valve assembly. The insert is retained in place by a shoulder formed on the downstream housing of the ball check valve assembly which is secured to the upstream housing by welding.
In accordance with more specific aspects of the invention, the insert preferably comprises a unitary, i.e., one-piece construction. The insert may be formed from the material sold under the trademark STELLITE.RTM., however, other, similar materials may be used in the practice of the invention, if desired. The technique used to join the downstream housing to the upstream housing to the ball check valve assembly preferably comprises either inertia welding or friction welding.